Showing 2 results for Mean Weight Diameter (mwd)
Mohammad Loghavi, Saeed Behnam,
Volume 2, Issue 4 (1-1999)
Abstract
The effects of three levels of soil moisture content (10 - 12, 13 - 15 and 16 - 18% d.b.) and three levels of plowing depth (15, 20 and 25 cm) on draft, specific draft, and drawbar power requirements of a 3 - bottom disk plow and on soil pulverization and inversion in a clay loam soil were investigated. The experimental design was a randomized complete block design with a 3 × 3 factorial. Except in soil inversion, the effect of soil moisture on all of the performance parameters mentioned, was highly significant. Mean values of draft, specific draft and drawbar power requirements and clod mean weight diameter were minimized at 13 - 15% and 16 - 18% soil moisture contents, respectively. The effect of plowing depth was highly significant only on draft and drawbar power requirement of disk plow, in such a way that the mean values of these two parameters were significantly increased with plowing depth, while specific draft showed only a mild decreasing trend. In order to provide a quantitative index to express the degree of soil pulverization by tillage implements, a tractor-pulled rotary sieve was designed and fabricated. With this apparatus, in-field determination of soil clod mean weight diameter (MWD) following plowing was possible. The results showed that the effect of soil moisture content on MWD was highly significant, such that, plowing at 10-12% moisture content produced the largest clods, whereas the effect of plowing depth on MWD was not significant. The decreasing trend of MWD with soil moisture content persisted to the highest moisture level studied (16 - 18%), in which the average clod MWD (33.8 mm) was about 72% smaller than those formed at 10-12% moisture content. The effects of plowing depth and soil m. c. on soil inversion by disk plow were not significant and the overall soil inversion was about 54% which was in agreement with those reported by other researchers.
M. R. Bahremand, M. Afyuni, M. A. Hajabbassi, Y. Rezaeinejad,
Volume 6, Issue 4 (1-2003)
Abstract
A field experiment was conducted to investigate the effects of sewage sludge and of time lapse after sludge application on soil physical properties. Four sewage sludge treatments (0, 25, 50, and 100 ton/ha) in a complete randomized block design with three replications were applied and mixed to a depth of 20 cm. Wheat was planted and soil physical properties were measured 23, 85, 148, and 221 days after sewage sludge application.
Sewage sludge application significantly increased MWD, hydraulic conductivity, final infiltration rate, moisture percentage at 1/3 and 15 bars, and plant available soil moisture, while it significantly decreased soil bulk density. In general, the best results obtained with the 100 ton/ha sewage sludge treatment. Time lapse after sewage sludge application caused soil physical properties to approach the values of the control. However, even 221 days after sludge application, the 50 and 100 ton/ha treatments had significantly different values compared with the control treatment. The results in this research show that sewage sludge can help to improve soil physical conditions and this effect persists over long periods. This effect is specially important with plant available soil moisture and infiltration.
